The valve stem extensions on our rear wheels are made with hard plastic tubes. One of ours from an inner tire apparently cracked - probably due to the constant vibrations over 12,000 miles. This cause the non-visible tire to deflate recently and the spinning around with no pressure destroyed the tire. The tires were rotated in June when we finished our 12K maiden journey so the failure happened in the last few hundred miles or so.

I don't know if this stem failure and the damage it caused is covered by the warranty but it seems like it should be.

I understand that there are similar extensions available that are made with SS tubing instead of plastic and we are replacing all of them with SS. Maybe FR could order the chassis this way or replace them at the factory. I don't know what the cost is but it is probably modest.

I had a similar problem but it turned out that the rubber nipples were rotten . To complicate matters, passenger tire nipples were used. The tire place said heavy duty nipples should be used on a 10k rv's
I replaced all with heavy duty and no problem since. (Rubber was rotten on others too, just not leaking yet)

Unless they changed, Forest River uses AirFlex airless extensions. Since they are airless, even if they crack, break, or get severed they shouldn't let the air out of the tire. They are a tube with a core down the middle. The core presses the valve stem at the tire (or, in the case of the outer dual tires on our 2012 Solera, the valve in the 135 degree metal extension attached to the tire valve) when filling the tire or checking the air.
I did experience air loss caused by the AirFlex extension moving around while driving and apparently working its core against the tire valve core. I have since tied up the extensions with wire ties to prevent.
As stated above, the tire valve stems - high pressure rubber stems on mine - seem to be the "weak link". Hard to find metal stems to replace them with - some have found "dually stems" that work. The Sprinter wheels are shaped in a way that prevents tightening most metal stems. The high pressure rubber stems are rated for the tire pressure and are what is recommended, but I experienced two valve failures (not catastrophic) with them. Tire shop said they had been "improperly installed". At my request, they found some metal stems that fit (barely) and replaced them.
I met Chuck Carvitto at a campground in central California - tire-man.iwvisp.com - who told me he had developed and sells metal valves for Sprinter duals. I had already found a place that put metal stems on mine - so I have not tried Chuck's devices.